1. Field of the Invention
The present invention pertains to the use of block copolymers containing a reactive monomer or monomers in two or more blocks via controlled free radical polymerization and use of the composition of matter as additives for the preparation of inorganic tubule-polymer composites.
2. Description of the Related Art
One of the parent inventions, described in U.S. patent application Ser. No. 11/711,206, provides in one aspect a polymer/clay nanocomposite material comprising an organic clay, a thermoplastic matrix, and a block copolymer as a compatibilizer, where the block copolymer has a composition that includes a first block, the first block comprising monomeric units of a functionalized acrylic monomer and/or a functionalized vinyl monomer and monomeric units of a vinyl monomer, and a second block, the second block comprising monomeric units of one or more vinyl monomers and monomeric units of the functionalized acrylic monomer and/or the functionalized vinyl monomer from the first block. A thermoset resin can be used instead of the thermoplastic resin.
In another aspect, U.S. patent application Ser. No. 11/711,206 provides a process for making a polymer/clay nanocomposite material, including mixing an organic clay and a block copolymer together in a ratio between the clay and the block copolymer of between 100:1 and 1:1000 to form a nanocomposite concentrate; mixing the nanocomposite concentrate and a functional polyolefin to form a polyolefin masterbatch; and mixing the polyolefin masterbatch and a thermoplastic polymer to obtain a polymer/clay nanocomposite material.
U.S. patent application Ser. No. 11/711,206 also describes a block copolymer having one block that is polar, hydrophylic and miscible in a clay slurry for use in clay production and another block that is nonpolar to increase the compatibility with a thermoplastic or thermoset resin. The block copolymer replaces conventional intercalate ammonium ions as well as conventional compatibilizers for a clay and thermoplastic or thermoset composite.
The present invention concerns an application where the parent invention is used in the preparation of inorganic tubule-polymer composites.
Silicate-polymer nanocomposites offer a number of significant advantages over traditional silicate-polymer composites. Conventional silicate-polymer composites usually incorporate a high content of the inorganic fillers—from 10 to as much as 50 weight percent (wt. %)—to achieve desired mechanical or thermal properties. Polymer nanocomposites can reach the desired properties, such as increased tensile strength, improved heat deflection temperature and flame retardance, with typically 3-5 wt. % of the nanofiller, producing materials with specific gravity close to that of the unfilled polymer, good surface appearance and better processability than traditional reinforcements. Other properties of nanocomposites such as optical clarity and improved barrier properties cannot be duplicated by conventionally-filled resins at any loading. (Bins & Associates, Plastics Additives & Compounding, 2002, 30-33.)
One general approach to prepare polymer nanocomposites is to employ planar layered clays, which consist of stacked aluminosilicate layers that can be separated. The clay layers, which are held together by electrostatic forces, cannot be broken into separate layers by simple shear, and for that reason, organic modification of the clay is necessary to achieve separation of the stacked clay layers. An organic modification that separates the stacked clay layers (intercalation and exfoliation) and that yields clay that has more affinity towards different polymeric matrices is actually a very active research area. U.S. Patent Application Pub. No. 2007/0106006, filed by Cooper at al. and incorporated by reference, referred to herein as “Cooper,” describes the benefits of using mineral nanotubes as fillers, in contrast to the difficulties (intercalation and exfoliation) encountered when planar layered clays are incorporated in polymeric matrices. Nanotubes do not require exfoliation, since they are discrete nanoparticles, and they offer additional functionality via the inner open space or cavity of the tube, particularly the ability to incorporate active chemical agents within the tubes or to coat the tube surfaces.
Halloysite, which is also known as endellite or to avoid confusion, halloysite-10A, is a mineral from the kaolin group that exists in the form of hollow tubes. See Thomas F. Bates, F. A. H., Ada Swineford, The American Mineralogist, 1950, 35, (7 and 8), 463-484. See also Joussein, E.; Petit, S.; Churchman, J.; Theng, B.; Righi, D.; Delvaux, B., Clay Minerals, 2005, 40, (4), 383-426. Halloysite is not an uncommon aluminosilicate clay in nature being found in many countries, including the United States of America, Brazil, China, France, Japan, South Korea and Turkey. Halloysite tubules from different regions and within samples vary in dimensions, but all are very small with typical outside diameters ranging from 10 nm to 500 nm, with a median value of 70 nm (according to Thomas F. Bates, F. A. H., Ada Swineford, The American Mineralogist, 1950, 35, (7 and 8), 463-484) or 200 nm, according to Cooper. The diameters of the holes range from 20 nm to 200 nm and average 40 nm. The lengths of halloysite tubules cover a wide range from 20 nm to more than 40,000 nm, and are typically about 1,200 nm, according to Cooper. The structure and chemical composition of halloysite (Al2Si2O5(OH)4.nH2O) is similar to that of kaolinite, dickite or nacrite but the unit layers in halloysite are separated by a monolayer of water molecules. As a result, hydrated halloysite has a basal (d001) spacing of 10 Å. Because the interlayer water is weakly held, halloysite-10 Å can readily dehydrate to give a corresponding halloysite-7 Å. Mismatch in the two-layered alignment of the tetrahedral sheet of silica bonded to the octahedral or gibbsite sheet of alumina causes the wall to curve into the cylindrical shape as explained by Bates et al. (Thomas F. Bates, F. A. H., Ada Swineford, The American Mineralogist, 1950, 35, (7 and 8), 463-484). Intercalated water may occur between the repetitive two-layered sheets comprising the spiral wall, which tends to be removed on drying. The indirect rehydratation of halloysite has been reported, forming an intermediary intersalation complex, followed by rinsing with water to remove the salt (Levis, S. R.; Deasy, P. B., International Journal of Pharmaceutics 2002, 243, 125-134). The inner and outer faces of the tubules walls carry normally a net negative charge, functioning as a polyvalent anion, whereas their edges are amphoteric with negative charge at high pH and positive charge at low pH. This unusual shape and charge distribution favors face-to-edge attachment in aqueous suspension below pH 6 and facilitates binding particularly of cations to the unreacted faces (Levis, S. R. and P. B. Deasy, International Journal of Pharmaceutics, 2002, 243, 125-134). Halloysite has a low specific surface area and cation exchange capacity, CEC (20-60 cmolckg−1). Adsorption of cations and anions by halloysite is influenced by the final concentration of the electrolyte solution. Both the CEC and anion exchange capacity (AEC) increase with salt concentration in solution.
Halloysite is capable of adsorbing different salts in the interlayer such as NH4-, K-, Cs- and Rb-salts, which gives rise to characteristic expansion of d001 spacing (Wada, K., Soil and Plant Food 1958, 4, (3), 137-144.). The adsorption of As(V) has also been reported. Organic compounds can also be adsorbed, either into the hollow lumen or spiral space of microtubules. Examples include molecules such as: ethanol, methanol, glycerol, ethylene glycol, acetone, acetonirile, dimethylsoulfoxide, hydrazine hydrate, formaldehyde, acetamide, urea, benzene, cyclohexane and n-hexane (Levis, S. R. and P. B. Deasy, International Journal of Pharmaceutics, 2002, 243, 125-134; Joussein, E.; Petit, S.; Churchman, J.; Theng, B.; Righi, D.; Delvaux, B., Clay Minerals, 2005, 40, (4), 383-426; Carrasco-Marin, F.; Domingo-García, M.; Fernández-Morales, I.; López-Garzón, F. J., Journal of Colloid and Interface Science 1988, 126, (2), 552-560). The use of hollow mineral tubules selected form the group consisting of halloysite, cylindrite, boulangerite and imogolite to adsorb active molecules (drugs, fertilizers, antifouling agents, pesticides pheromones, biocide agents, antiscale, anticorrosion agents and combinations thereof) and then release them in a controlled fashion has also been described in several patents. See U.S. Pat. Nos. 4,019,934; 5,651,976; 5,705,191; and 6,401,816. Halloysite's lumen has also been modified to include cosmetic products that are released in a controlled fashion, including compounds such as moisturizing agents, local anesthetics, antiseptics, perfumes, skin repair ingredients and hair dissolver materials (U.S. Patent Application Pub. No. 2007/0292459). Halloysite has been treated with cationic polymeric coatings such as chitosan, polyethyleneimine related to drug delivery applications (Levis, S. R.; Deasy, P. B., International journal of pharmaceutics 2003, 253, (1-2), 145-157) or biodegradable biofouling release purposes (U.S. Patent Application Pub. No. 2007/0059273).
Halloysite has also been used, in combination with other clays, such as attapulguite, as catalyst support for the conversion of hydrocarbonaceous feedstocks, specially for demetalizing and hydroprocessing process (U.S. Pat. No. 4,364,857) and as a template for metal nanoparticles and wires deposition (Fu, Y.; Zhang, L., Journal of Solid State Chemistry 2005, 178, 3595-3600).
Compared to other microtubules such as carbon nanotubules, halloysite has the advantage of being available worldwide at low cost. Halloysite can be obtained, for example, from Atlas Mining Company of Osburn, Id., USA.
Cooper described halloysite as a useful constituent of polymeric composites for the purpose of thermal improvement and mechanical properties improvement. See also Du, M.; Guo, B.; Jia, D., European Polymer Journal, 2006, 42, 1362-1369. In the case of nylon, halloysite has been modified with benzalkonium chloride before blending (Cooper's example 1) to obtain an improvement in modulus, but in the case of polypropylene, the use of compatibilizers such as maleic anhydride-graft-polypropylene copolymer did not improve the mechanical properties of the composite (Cooper's example 2). In order to improve the compatibility between polypropylene and halloysite, Ning et. al. introduced alkyl substituted quaternary ammonium, obtaining an improvement in the modulus when HNT is loaded in a 10% wt. Ning, N.-Y.; Yina, Q.-J.; Luoa, F.; Zhanga, Q.; Dua, R.; Fu, Q., Polymer 2007, 48, (25), 7374-7384. In the case of thermoset polymers, the use of natural halloysite in epoxy nanocomposites has been reported to increase the izod impact by Yea et. Al. (Yea, Y.; Chena, H.; Wua, J.; Yeb, L., Polymer 2007, 48, 6426-6433).